An earlier patent owned by the inventor of the present invention, U.S. Pat. No. 5,697,071, disclosed a mobile phone holder structure, including an upper casing member and a lower casing member, each having an inside surface on which a plurality of parallel-arranged guiding slots are formed. Two removable clamps are located on the two sides of the upper and lower casings. The bottom of the clamps forms engaging stripes to be selectively slidably receivable within the guiding slots of the upper and lower casing members. Each of the clamp members has resilient holding sections extending therefrom to define a space for receiving and holding therein a mobile phone. The open end of the casings allows the clamp members to be removed from the casing members and re-inserted into another guiding slot so as to change the distance between the clamp members and thus adapted to hold phones of difference sizes. While many advantages provided by the earlier invention are still valid, several issues have been raised:    1. The holding force between the two clamps weakens when the distance between right clamp and the left clamp is closer to the maximum distance. This is because only the central part is tightly fastened when the upper and the lower casing members are engaged. To avoid the interfering the insertion of the clamps, no additional fastening elements are added. Therefore, the holding force at the edges of the upper and lower casings is only provided by the strength of the material, usually made of plastics. When the right and the left clamps are moved to the rightmost and leftmost positions respectively, the edges of the plastic upper and lower casings are prone to be stretched and deformed when the outward force between the right and left clamps is too large. In this manner, the engaging stripes can be easily disengaged from the guiding slots so that the clamps can no longer clamp to hold the device. The longer the apparatus is in use, the likelihood of this situation is increased.    2. The number of components in the earlier invention is larger and screws are required to fasten components, leading to higher manufacturing cost.    3. The size is bulky and the design appears less streamlined. Therefore, the inventor has redesigned a new apparatus for holding portable devices of different sizes.